df5.apply(lambda row: row.sum(), axis=1)

# H2OFrame:
#        C1
# ---------
# -0.388512
#  1.67669
# -2.56216
# -0.277616
#  1.13655
# -0.575992
# -3.49258
#  0.776883
# -0.778604
#  2.30617
#
# [100 rows x 1 column]